As one type of constructed wetlands, a subsurface flow wetland exerts synergistic effects of physical, chemical and biological purification of the substrate due to its small-scale land occupation. Subsurface flow wetland is efficient in removing organic matter and nutrients (such as nitrogen and phosphorus nutrients) in sewage, and greatly enhances sewage treatment capacity. Therefore, subsurface flow wetland is widely used in the practice of sewage treatment.
The oxygen content in the substrate of subsurface flow wetlands is relatively low, and oxygen is deficient inside the wetlands, which can easily result in lower removal rates for total nitrogen (TN), chemical oxygen demand (COD), and biochemical oxygen demand (BOD). Currently available solutions for this problem include inserting PVC pipes into the substrate of the wetlands in order to use the pressure difference created by water flow to increase re-aeration capacity of the substrate directly by the atmosphere. Another solution is by building a water-fall waterscape based on the terrain in order to increase the concentration of dissolved oxygen in the substrate of the wetlands. Although these methods have achieved good application effects, during the operation of subsurface flow wetlands, these current methods cannot generate a sufficient unit re-aeration amount of the substrate of subsurface flow wetlands to satisfy practical demands, due to the long hydraulic retention time and unstable water pressures. These limitations adversely affect the purification effects of subsurface flow wetlands. Yet another existing method delivers oxygen through PVC pipes inserted in the substrate by a blower device actuated by a motor. Although this method may satisfy practical demands and achieve better re-aeration effects than the methods using water pressure or water-fall waterscape, the cost thereof is relatively high and the implementing process thereof is complex. Because sufficient oxygen in the wetland substrate is one of the main factors increasing the purification efficiency by the wetlands, there is an urgent need to increase efficiency of re-aeration of the substrate and reduce the corresponding cost in order to keep the sustainable operation of the constructed wetlands. There is no report about such technique currently.